1. Field of the Invention
The present invention relates to a method of checking pallets or articles to be worked fed into a working process and an apparatus for practicing same, and more particularly to a method of checking pallets or articles to be worked and an apparatus for practicing same in which an average diameter of a hole of a pallet or an article to be worked automatically measured by means of three displacement detectors mounted on the body of an apparatus for measuring a diameter of a hole is used as a checking means.
2. Prior Arts
Various methods of measuring an average diameter of a hole of an article to be worked in a working process in a machining center are proposed and being practically used. One is a method of measuring an average diameter of a hole of an article to be worked by simultaneously bringing three displacement detectors into contact with the inside circumferential surface of said hole to be measured, as disclosed in the specification of U.S. Pat. No. 3191294. Another is a method of calculating a diameter of a hole, in which the whole measuring apparatus is displaced toward the direction of an axis of abscissa and the direction of an axis of ordinate of the hole from the central position of said hole in said hole of which a diameter is to be measured, the magnitude of the displacement of the measuring apparatus until a pointed end of a contact needle is brought into contact with the inside circumferential surface of the hole to be measured being detected, and a diameter of the hole is calculated from the magnitude of the displacement of said measuring apparatus in the direction of X-axis and that in the direction of the Y-axis, as disclosed in Japanese Patent Laid-Open No. Sho 49-20772 or Japanese Patent Laid-Open No. Sho 50-43580.
The three-point simultaneously contacting method is a method in which a measuring apparatus provided with a contact needle elastically projecting on the periphery of a cylindrical bar is inserted into a hole to be measured of an article to be worked, and a diameter of the hole is measured on the basis of whether the contact needle is withdrawn or not, but since it is difficult to set the projection of the contact needle to a large magnitude, this method has a disadvantage that a measuring range is limited. Accordingly, in order to apply this method to the measurement of various kinds of diameter of a hole, the large number of measuring apparatus must be prepared in accordance with diameters of a hole and a remarkable disadvantage is accompanied by mounting all of these measuring apparatus on a tool-magazine.
On the contrary, the second method is superior to the first method in that a measuring range is wide, so it is not necessary to always prepare a large number of measuring apparatus. According to this second method, it is, however, necessary to displace a measuring apparatus from the central position of a hole in the radial direction in the measurement of a diameter of a hole, so it takes a measuring time longer than that in the first method by a time required for the displacement of the measuring apparatus. In addition, according to this second method, since an average diameter of a hole of an article to be worked is calculated from the magnitude of the displacement of a measuring apparatus, it shows a disadvantage that an accuracy of measurement of a diameter of a hole is greatly dependent upon an accuracy of displacement of a measuring apparatus.
On the other hand, in order to smoothly practice an unattended continuous working by means of a machining center as above described, it is necessary to adopt a checking system which can correctly distinguish the characteristics of pallets or articles to be worked fed into said machining center. However, a checking means, which is practically usable, meeting such an object, and having a high accuracy of discrimination, has been hardly proposed heretofore. Described in more detail, in the practical mechanical working line, a plurality of pallets are fed into one machining center and an appointed pallet is called and then the NC program corresponding to the work for said pallet is called to carry out the appointed mechanical work. Since the operation of mounting an article to be worked on a pallet is manually carried out although the above described actions are all automatically carried out, the faculty for checking whether a pallet or an article to be worked correctly corresponds to a NC program or not is required. According to the conventional distinguishing-checking methods, a dog and the like mounted on a pallet have been detected by a limit switch and a pallet or an article to be worked placed on said pallet has been distinguished by the obtained two-value signal (ON-OFF). In this case, since the number of limit switches is increased with an increase of the number of pallets, a practical disadvantage has been found with respect to a large space required for mounting limit switches thereon. In addition, since the setting of a dog corresponding to said two-value signal is manually carried out, it takes an increasingly longer time to set a dog with an increase of the number of pallets, whereby the danger of missetting is increased.